The investigation proposed in this year's grant is a continuation of a study of ion selectivity by a phospholipid channel, and in particular an investigation of a theory that access to the K ion active site of transport Na ion K ion ATPase is gated by a K ion selective phospholipid channel. Thus far there is a good correlation between ion selectivity of the K ion active site of Na ion K ion ATPase as studied by the overall hydrolysis of ATP and by the partial reactions of the enzyme. The effects of other cations such as Ca ions and Mg ions on the in vitro phospholilid channels are also paralleled by the defects of these cations on the overall hydrolysis of ATP and on the partial reactions of the enzyme. However the effects of Ca ions and Mg ions are much more complicated, involving what appear to be regulatory functions. Basic data have been obtained for the effects of these cations on the enzyme. This will be continued in an effort to determine whether such effects also involve the phospholipids of the enzyme. PI will also pursue data which suggests that the entry of Na ion into the enzyme could also be gated by a selective pore.